A gyratory crusher of the above-mentioned type may be utilized in order to crush hard material, such as pieces of rock material. An example of such a crusher is disclosed in WO 93/14870. Upon starting-up crushing in a gyratory crusher, the motor that drives the shaft having the crushing head mounted thereon is first started and then supply of material is commenced in a gap between an inner and an outer shell. It has turned out that gyratory crushers occasionally get stuck, i.e., the inner shell is jammed against the outer shell when the material initially reaches the gap between the inner and the outer shell. For this reason, a safety factor is utilized which means that the gap width between the inner and the outer shell is set to a larger value in the start than what is expected to be suitable for continuous operation at the material supply in question. When the crushing has become stable, the gap is decreased to the desired value.
The above-described method for starting a crusher may to a certain degree decrease the risk of mechanical damage on the crusher during the starting-up but entails that it takes a long time to reach optimal crushing conditions in the crusher.